Piezo electrophoretic display

ABSTRACT

Provided herein is an electro-optic display having a layer of electrophoretic material, a first conductive layer, and a piezoelectric material positioned between the layer of electrophoretic material and the first conductive layer, the piezoelectric material overlaps with a portion of the layer of electrophoretic material, and a portion of the first conductive layer overlaps with the rest of the electrophoretic material.

REFERENCE TO RELATED APPLICATIONS

This application is related and claims priority to U.S. ProvisionalApplication 62/673,092 filed on May 17, 2018. This application is alsorelated to U.S. Provisional Application 62/727,033 filed on Sep. 5,2018.

The entire disclosures of the aforementioned applications are hereinincorporated by reference.

SUBJECT OF THE INVENTION

The subject matter disclosed herein relates to piezo electrophoreticdisplays which may be activated or driven without being connected to apower source, and methods for their manufacture.

BACKGROUND

Non-emissive displays convey information using contrast differences,which are achieved by varying the reflectance of different frequenciesof light; they are thus distinct from traditional emissive displays,which stimulate the eye by emitting light. One type of non-emissivedisplay is an electrophoretic display, which utilizes the phenomenon ofelectrophoresis to achieve contrast. Electrophoresis refers to movementof charged particles in an applied electric field. When electrophoresisoccurs in a liquid, the particles move with a velocity determinedprimarily by the viscous drag experienced by the particles, theircharge, the dielectric properties of the liquid, and the magnitude ofthe applied field.

An electrophoretic display utilizes charged particles of one colorsuspended in a dielectric liquid medium of a different color (that is,light reflected by the particles) is absorbed by the liquid. Thesuspension is housed in a cell located between (or partly defined by) apair of oppositely disposed electrodes, one of which is transparent.When the electrodes are operated to apply a DC or pulsed field acrossthe medium, the particles migrate toward the electrode of opposite sign.The result is a visually observable color change. In particular, when asufficient number of the particles reach the transparent electrode,their color dominates the display; if the particles are drawn to theother electrode, however, they are obscured by the color of the liquidmedium, which dominates instead.

Many electrophoretic displays are bi-stable: their state persists evenafter the activating electric field is removed. This is generallyachieved via residual charge on the electrodes and van der Waalsinteractions between the particles and the walls of the electrophoreticcell. The driving of an electrophoretic display requires a power source,such as a battery to provide power to the display and/or its drivingcircuitry. The power source may be a driver IC in order to generate anelectric field. The electric field may also need to be enhanced by acircuitry. In any case, a physical connection through wires is requiredto attach the power source to the electrophoretic display and itsdriving circuitry.

SUMMARY

According to one aspect of the subject matter disclosed herein, anelectro-optic display may include a layer of electrophoretic material; afirst conductive layer; and a piezoelectric material positioned betweenthe layer of electrophoretic material and the first conductive layer,the piezoelectric material overlaps with a portion of the layer ofelectrophoretic material, and a portion of the first conductive layeroverlaps with the rest of the electrophoretic material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of an exemplary electrophoretic displayin accordance with the subject matter disclosed herein;

FIG. 2a is another cross sectional view of the display illustrated inFIG. 1;

FIG. 2B is an equivalent circuit model of the display illustrated inFIGS. 1 and 2A;

FIG. 3A is a cross sectional view of another exemplary display inaccordance with the subject matter disclosed herein;

FIG. 3B is a cross sectional view along the line C1 of the displayillustrated in FIG. 3A;

FIG. 3C is a cross sectional view along the line C2 of the displayillustrated in FIG. 3A;

FIG. 3D illustrate yet another embodiment of a display in accordancewith the subject matter presented herein;

FIG. 4 is a cross sectional view of yet another exemplary display inaccordance with the subject matter disclosed herein;

FIG. 5 is a cross section view of another exemplary display inaccordance with the subject matter disclosed herein;

FIG. 6 illustrates one embodiment of a piezo electrophoretic displaywith a jigsaw pattern in accordance with the subject matter disclosedherein;

FIG. 7 illustrates yet another embodiment of a piezo electrophoreticdisplay having a pattern in accordance with the subject matter disclosedherein;

FIG. 8 illustrates a piezo electrophoretic display in accordance withthe subject matter disclosed herein being used as part of a currencybill for anti-counterfeiting purposes;

FIG. 9 illustrate a cross section of yet another embodiment of apiezoelectric display in accordance with the subject matter disclosedherein;

FIG. 10 is a cross sectional view of a piezoelectric display inaccordance with the subject matter disclosed herein having a barrierlayer,

FIG. 11A is a top view of a micro-cell layer,

FIG. 11B is a cross sectional view of the micro-cell layer illustratedin FIG. 10A;

FIGS. 12A and 12B illustrate another embodiment of an electrophoreticdisplay in accordance with the subject matter disclosed herein;

FIGS. 13A and 13B illustrate yet another embodiment of anelectrophoretic display in accordance with the subject matter disclosedherein;

FIG. 14A illustrate an addition embodiment of an electrophoretic displaywith printed images or shapes in accordance with the subject matterdisclosed herein;

FIGS. 14B-14E illustrate the display of FIG. 14A in use in accordancewith the subject matter disclosed herein;

FIG. 15A illustrate yet another embodiment of an electrophoretic displaywith printed images or shapes in accordance with the subject matterdisclosed herein; and

FIGS. 15B-15C illustrate the display of FIG. 15A in use in accordancewith the subject matter disclosed herein.

DETAILED DESCRIPTION

The term “electro-optic”, as applied to a material or a display, is usedherein in its conventional meaning in the imaging art to refer to amaterial having first and second display states differing in at leastone optical property, the material being changed from its first to itssecond display state by application of an electric field to thematerial. Although the optical property is typically color perceptibleto the human eye, it may be another optical property, such as opticaltransmission, reflectance, luminescence or, in the case of displaysintended for machine reading, pseudo-color in the sense of a change inreflectance of electromagnetic wavelengths outside the visible range.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin U.S. Pat. No. 7,170,670 that some particle-based electrophoreticdisplays capable of gray scale are stable not only in their extremeblack and white states but also in their intermediate gray states, andthe same is true of some other types of electro-optic displays. Thistype of display is properly called “multi-stable” rather than bistable,although for convenience the term “bistable” may be used herein to coverboth bistable and multi-stable displays.

The term “gray state” is used herein in its conventional meaning in theimaging art to refer to a state intermediate two extreme optical statesof a pixel, and does not necessarily imply a black-white transitionbetween these two extreme states. For example, several of the E Inkpatents and published applications referred to below describeelectrophoretic displays in which the extreme states are white and deepblue, so that an intermediate “gray state” would actually be pale blue.Indeed, as already mentioned, the change in optical state may not be acolor change at all. The terms “black” and “white” may be usedhereinafter to refer to the two extreme optical states of a display, andshould be understood as normally including extreme optical states whichare not strictly black and white, for example, the aforementioned whiteand dark blue states. The term “monochrome” may be used hereinafter todenote a display or drive scheme which only drives pixels to their twoextreme optical states with no intervening gray states.

The term “pixel” is used herein in its conventional meaning in thedisplay art to mean the smallest unit of a display capable of generatingall the colors which the display itself can show. In a full colordisplay, typically each pixel is composed of a plurality of sub-pixelseach of which can display less than all the colors which the displayitself can show. For example, in most conventional full color displays,each pixel is composed of a red sub-pixel, a green sub-pixel, a bluesub-pixel, and optionally a white sub-pixel, with each of the sub-pixelsbeing capable of displaying a range of colors from black to thebrightest version of its specified color.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedby applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845.Nanochromic films of this type are also described, for example, in U.S.Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium isalso typically bistable.

Another type of electro-optic display is an electro-wetting displaydeveloped by Philips and described in Hayes, R. A., et al., “Video-SpeedElectronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003).It is shown in U.S. Pat. No. 7,420,549 that such electro-wettingdisplays can be made bistable.

One type of electro-optic display, which has been the subject of intenseresearch and development for a number of years, is the particle-basedelectrophoretic display, in which a plurality of charged particles movethrough a fluid under the influence of an electric field.Electrophoretic displays can have attributes of good brightness andcontrast, wide viewing angles, state bistability, and low powerconsumption when compared with liquid crystal displays.

As noted above, electrophoretic media require the presence of a fluid.In most prior art electrophoretic media, this fluid is a liquid, butelectrophoretic media can be produced using gaseous fluids; see, forexample, Kitamura, T., et al., “Electrical toner movement for electronicpaper-like display”, IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y.,et al., “Toner display using insulative particles chargedtriboelectrically”, IDW Japan 2001, Paper AMD4-4). See also U.S. Pat.Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic mediaappear to be susceptible to the same types of problems due to particlesettling as liquid-based electrophoretic media, when the media are usedin an orientation which permits such settling, for example in a signwhere the medium is disposed in a vertical plane. Indeed, particlesettling appears to be a more serious problem in gas-basedelectrophoretic media than in liquid-based ones, since the lowerviscosity of gaseous suspending fluids as compared with liquid onesallows more rapid settling of the electrophoretic particles.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporationdescribe various technologies used in encapsulated electrophoretic andother electro-optic media. Such encapsulated media comprise numeroussmall capsules, each of which itself comprises an internal phasecontaining electrophoretically-mobile particles in a fluid medium, and acapsule wall surrounding the internal phase. Typically, the capsules arethemselves held within a polymeric binder to form a coherent layerpositioned between two electrodes. The technologies described in thesepatents and applications include:

-   -   (a) Electrophoretic particles, fluids and fluid additives; see        for example U.S. Pat. Nos. 7,002,728 and 7,679,814;    -   (b) Capsules, binders and encapsulation processes; see for        example U.S. Pat. Nos. 6,922,276 and 7,411,719;    -   (c) Films and sub-assemblies containing electro-optic materials;        see for example U.S. Pat. Nos. 6,982,178 and 7,839,564;    -   (d) Backplanes, adhesive layers and other auxiliary layers and        methods used in displays; see for example U.S. Pat. Nos.        7,116,318 and 7,535,624;    -   (e) Color formation and color adjustment; see for example U.S.        Pat. Nos. 7,075,502 and 7,839,564;    -   (f) Methods for driving displays; see for example U.S. Pat. Nos.        7,012,600 and 7,453,445;    -   (g) Applications of displays; see for example U.S. Pat. Nos.        7,312,784 and 8,009,348;    -   (h) Non-electrophoretic displays, as described in U.S. Pat. Nos.        6,241,921; 6,950,220; 7,420,549 and 8,319,759; and U.S. Patent        Application Publication No. 2012/0293858;    -   (i) Microcell structures, wall materials, and methods of forming        microcells; see for example U.S. Pat. Nos. 7,072,095 and        9,279,906; and    -   (j) Methods for filling and sealing microcells; see for example        U.S. Pat. Nos. 7,144,942 and 7,715,088.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display, inwhich the electrophoretic medium comprises a plurality of discretedroplets of an electrophoretic fluid and a continuous phase of apolymeric material, and that the discrete droplets of electrophoreticfluid within such a polymer-dispersed electrophoretic display may beregarded as capsules or microcapsules even though no discrete capsulemembrane is associated with each individual droplet; see for example,the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes ofthe present application, such polymer-dispersed electrophoretic mediaare regarded as sub-species of encapsulated electrophoretic media.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to SipixImaging, Inc.

Although electrophoretic media are often opaque (since, for example, inmany electrophoretic media, the particles substantially blocktransmission of visible light through the display) and operate in areflective mode, many electrophoretic displays can be made to operate ina so-called “shutter mode” in which one display state is substantiallyopaque and one is light-transmissive. See, for example, U.S. Pat. Nos.5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and6,184,856. Dielectrophoretic displays, which are similar toelectrophoretic displays but rely upon variations in electric fieldstrength, can operate in a similar mode; see U.S. Pat. No. 4,418,346.Other types of electro-optic displays may also be capable of operatingin shutter mode. Electro-optic media operating in shutter mode may beuseful in multi-layer structures for full color displays; in suchstructures, at least one layer adjacent the viewing surface of thedisplay operates in shutter mode to expose or conceal a second layermore distant from the viewing surface.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating, meniscus coating; spin coating; brush coating; air knifecoating, silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes;electrophoretic deposition (See U.S. Pat. No. 7,339,715); and othersimilar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed, using a variety ofmethods, the display itself can be made inexpensively.

Other types of electro-optic materials may also be used in the presentinvention.

An electrophoretic display normally comprises a layer of electrophoreticmaterial and at least two other layers disposed on opposed sides of theelectrophoretic material, one of these two layers being an electrodelayer. In most such displays both the layers are electrode layers, andone or both of the electrode layers are patterned to define the pixelsof the display. For example, one electrode layer may be patterned intoelongate row electrodes and the other into elongate column electrodesrunning at right angles to the row electrodes, the pixels being definedby the intersections of the row and column electrodes. Alternatively,and more commonly, one electrode layer has the form of a singlecontinuous electrode and the other electrode layer is patterned into amatrix of pixel electrodes, each of which defines one pixel of thedisplay. In another type of electrophoretic display, which is intendedfor use with a stylus, print head or similar movable electrode separatefrom the display, only one of the layers adjacent the electrophoreticlayer comprises an electrode, the layer on the opposed side of theelectrophoretic layer typically being a protective layer intended toprevent the movable electrode damaging the electrophoretic layer.

In yet another embodiment, such as described in U.S. Pat. No. 6,704,133,electrophoretic displays may be constructed with two continuouselectrodes and an electrophoretic layer and a photoelectrophoretic layerbetween the electrodes. Because the photoelectrophoretic materialchanges resistivity with the absorption of photons, incident light canbe used to alter the state of the electrophoretic medium. Such a deviceis illustrated in FIG. 1. As described in U.S. Pat. No. 6,704,133, thedevice of FIG. 1 works best when driven by an emissive source, such asan LCD display, located on the opposed side of the display from theviewing surface. In some embodiments, the devices of U.S. Pat. No.6,704,133 incorporated special barrier layers between the frontelectrode and the photoelectrophoretic material to reduce “darkcurrents” caused by incident light from the front of the display thatleaks past the reflective electro-optic media.

The aforementioned U.S. Pat. No. 6,982,178 describes a method ofassembling a solid electro-optic display (including an encapsulatedelectrophoretic display) which is well adapted for mass production.Essentially, this patent describes a so-called “front plane laminate”(“FPL”) which comprises, in order, a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer, and a release sheet. Typically, the light-transmissiveelectrically-conductive layer will be carried on a light-transmissivesubstrate, which is preferably flexible, in the sense that the substratecan be manually wrapped around a drum (say) 10 inches (254 mm) indiameter without permanent deformation. The term “light-transmissive” isused in this patent and herein to mean that the layer thus designatedtransmits sufficient light to enable an observer, looking through thatlayer, to observe the change in display states of the electro-opticmedium, which will normally be viewed through theelectrically-conductive layer and adjacent substrate (if present); incases where the electro-optic medium displays a change in reflectivityat non-visible wavelengths, the term “light-transmissive” should ofcourse be interpreted to refer to transmission of the relevantnon-visible wavelengths. The substrate will typically be a polymericfilm, and will normally have a thickness in the range of about 1 toabout 25 mil (25 to 634 μm), preferably about 2 to about 10 mil (51 to254 μm). The electrically-conductive layer is conveniently a thin metalor metal oxide layer of, for example, aluminum or ITO, or may be aconductive polymer. Poly (ethylene terephthalate) (PET) films coatedwith aluminum or ITO are available commercially, for example as“aluminized Mylar” (“Mylar” is a Registered Trade Mark) from E.I. duPont de Nemours & Company, Wilmington Del., and such commercialmaterials may be used with good results in the front plane laminate.

Assembly of an electro-optic display using such a front plane laminatemay be effected by removing the release sheet from the front planelaminate and contacting the adhesive layer with the backplane underconditions effective to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane. This processis well-adapted to mass production since the front plane laminate may bemass produced, typically using roll-to-roll coating techniques, and thencut into pieces of any size needed for use with specific backplanes.

U.S. Pat. No. 7,561,324 describes a so-called “double release sheet”which is essentially a simplified version of the front plane laminate ofthe aforementioned U.S. Pat. No. 6,982,178. One form of the doublerelease sheet comprises a layer of a solid electro-optic mediumsandwiched between two adhesive layers, one or both of the adhesivelayers being covered by a release sheet. Another form of the doublerelease sheet comprises a layer of a solid electro-optic mediumsandwiched between two release sheets. Both forms of the double releasefilm are intended for use in a process generally similar to the processfor assembling an electro-optic display from a front plane laminatealready described, but involving two separate laminations; typically, ina first lamination the double release sheet is laminated to a frontelectrode to form a front sub-assembly, and then in a second laminationthe front sub-assembly is laminated to a backplane to form the finaldisplay, although the order of these two laminations could be reversedif desired.

U.S. Pat. No. 7,839,564 describes a so-called “inverted front planelaminate”, which is a variant of the front plane laminate described inthe aforementioned U.S. Pat. No. 6,982,178. This inverted front planelaminate comprises, in order, at least one of a light-transmissiveprotective layer and a light-transmissive electrically-conductive layer;an adhesive layer; a layer of a solid electro-optic medium; and arelease sheet. This inverted front plane laminate is used to form anelectro-optic display having a layer of lamination adhesive between theelectro-optic layer and the front electrode or front substrate; asecond, typically thin layer of adhesive may or may not be presentbetween the electro-optic layer and a backplane. Such electro-opticdisplays can combine good resolution with good low temperatureperformance.

The photoelectrophoretic properties of certain pigments were recognizedsome time ago. For example U.S. Pat. No. 3,383,993 discloses aphotoelectrophoretic imaging apparatus that could be used to reproduceprojected images on a medium, typically a transparent electrode, such asITO. The photoelectrophoretic process described in the '993 patent, andother related patents by Xerox Corporation, was not reversible, however,because the photoelectrophoretic process involved thephotoelectrophoretic particles migrating to an “injecting electrode”where they would become attached to the electrode. Because of the lackof reversibility, as well as the cost and complication of the setup,this phenomenon was not commercialized widely.

The subject matter presented herein relates to several piezoelectrophoretic display structural designs which do not need a powersupply (e.g., battery or wired power supply etc.) in order for theelectrophoretic display to operate. The assembly of such anelectrophoretic display is therefore simplified.

Piezoelectricity is the charge which accumulates in a solid material inresponse to applied mechanical stress. Suitable materials for thesubject matter disclosed herein may include polyvinylidene fluoride(PVDF), quartz (SiO₂), berlinite (AlPO₄), gallium orthophosphate(GaPO₄), tourmaline, barium titanate (BaTiO₃), lead zirconate titanate(PZT), zinc oxide (ZnO), aluminum nitride (AlN), lithium tantalite,lanthanum gallium silicate, potassium sodium tartrate and any otherknown piezo materials.

Some aspects of the subject matter presented herein utilizes thepiezoelectricity to drive the pigments of an electrophoretic material,to change the color of the electrophoretic material when viewed from aviewing surface. For example, by bending or introduce stress to a pieceof piezo material, voltage may be generated and this voltage can beutilized to cause movement of the color pigments of the electrophoreticmaterial. As used herein, the term “contrast ratio” (CR) for anelectro-optic display (e.g., an electrophoretic display) is defined asthe ratio of the luminance of the brightest color (white) to that of thedarkest color (black) that the display is capable of producing. Normallya high contrast ratio, or CR, is a desired aspect of a display.

FIG. 1 illustrates a cross sectional view of an exemplary electro-opticdisplay 100 using a piezo material 102 to drive an electrophoreticmaterial (EPD) film 104 in accordance with the subject matter disclosedherein. In this embodiment, the piezo film 102 may be laminated to aportion of the EPD film 104, and a conductive adhesive material (e.g.,copper tape) may be used to cover up the piezo film 102 and the rest ofthe EPD film 104 as illustrated in FIGS. 1 And 2A. In some embodiments,the conductive adhesive material may function as an electrode 2 108 andbe affixed to a substrate (not shown). In some other embodiments, theelectrode 2 108 may function as a pixel electrode for modulating avoltage potential across the EPD film 104 for displaying colors orimages (e.g., by changing the graytones of the EPD film 104).Furthermore, opposite to the electrode 2 108, an electrode 1 106 mayoverlap with the EPD film layer 104. In yet another embodiment, the EPDfilm 104 may be fabricate onto the electrode 1 106 to begin with. Forexample, electrode 1 106 may firstly be patterned to include micro-cellstructures where electrophoretic fluid with electrophoretic particlesmay be embossed into the micro-cell structure to form an EPD film layer.For which the details will be described in FIGS. 9 and 11A-B below. Inthis configuration, the EPD film 104 and the electrode 1 106 may be ofan integrated structure. In some other embodiments, both the electrode 1106 and electrode 2 108 may be transparent, or either electrode 1 106 orelectrode 2 108 may be transparent, such that display 100 may be viewedfrom either directions.

In practice, the CR of the electro-optic display 100 may differdepending on the ratio of the EPD film 104 surface area A1 110 (i.e.,the portion of EPD film 104 that is overlaps with or covered by or indirect contact with the piezo material 102) compared to that of area A2112 (i.e., the portion of EPD film 104 that is overlapped with orcovered by electrode 2 108), as illustrated in FIG. 1. Experimentalresult of the CR are shown below in Table 1—

TABLE 1 Display CR vs Piezo Film Surface Area Ratio of EPD film on piezofilm to that Response of display on conductive adhesive on strain change0 Contrast ratio: 1.7 1:2 Contrast ratio: 2 1:1 Contrast ratio: 5 2:1Contrast ratio: 7

As shown in FIG. 1, a display such as the one illustrated in FIG. 1 mayimprove its CR by reducing the overall surface area (e.g., A2) of theEPD film 104 that overlaps or is on electrode 2 108 (i.e., conductiveadhesive material). The CR improved from 2, when the ratio of EPD film104 that is on piezo film 102 (e.g., A1) to that is on electrode 2 108(e.g., A2) is 1:2, to 7 when the ratio became 2:1. In some embodiments,to further improve the CR, the width of either electrode 1 106 orelectrode 2 108 may be reduced such that whatever physical stressapplied may be applied to the longer side of electrode 2 108 in avertical direction.

FIG. 2B illustrates an exemplary equivalent circuit of the display 100shown in FIG. 1 in accordance with the subject matter disclosed herein.Portion of the EPD film 104 in contact with the piezo film 102 may havean electrical resistance value R1 and the portion covered by electrode 2108 may have an electrical resistance value R2. In practice, voltagegenerated by the piezo film 104 may be split between R1 and R2 placed ina series configuration. In some embodiments, there may be an adhesivelayer between the piezoelectric film 102 and the EPD film layer 104,where the adhesive layer may have a resistivity value of roughly 10⁸Ohm*cm, and preferably less than 10¹² Ohm*cm.

In another embodiment in accordance with the subject matter disclosedherein, instead of having a piezo film directly laminated onto oroverlapping with an EPD film as shown in FIGS. 1 and 2A, a piezo film302 may be laminated onto a semi-conductive or high-resistive layer 304,and then laminate the semi-conductive or high-resistive layer 304 ontoan electrode 1 layer 306, as shown in FIG. 3A. In this configuration,the semi-conductive or high-resistive layer 304 replaces portions of theEPD film 308 on top of the piezo film 302, thereby reducing the overallthickness of the display, as well as preventing a fast dissipation ofcharges across the piezo film 302 so the locally produced charges (bythe piezo film 302) may be effectively and efficiently applied onto theEPD film 308, which results in an improvement in the display CR.Illustrated below in Table 2 is a comparison of the resistivity level ofthe semi-conductive layer 304 and the resulting CR. As shown, an optimumCR ratio of 12 may be achieved when the semi-conductive layer 304 has aresistivity of 10⁸ Ohm*cm.

TABLE 2 Display CR vs. Resistance Resistivity of material in betweenResponse of display electrode 1 and piezo film (Ohm*cm) on strain change10² Contrast ratio: 1.7 10⁸ Contrast ratio: 12 >10¹²  Contrast ratio: 1(no response)

Furthermore, display CR may be optimized by adjust the resistance valueof the semi-conductive layer 304. For example, at a resistance range ofapproximately 10⁸ (Ohm*cm), the display CR of 12 may be achieved. Inanother embodiment, the resistance of the electrode 1 layer 306 may beat approximately 450 ohm/sq, where the resistance of an electrode 2layer 310 may be at 0.003 ohm/sq, the EPD film 308 may have a resistanceof approximately 10⁷ to 10⁸ oh, and the piezo material 302 may have aresistance of 10¹³ to 10¹⁴ ohm.

FIGS. 3B and 3C are cross sectional views of the display illustrated inFIG. 3A. FIG. 3B shows the display cross-section along the C1 line andFIG. 3C shows the display cross-section along the C2 line. In practice,only the EPD portion 308 of the display may be made visible to a user,while the piezo film portion may be covered up. As also illustrated inFIGS. 3B and 3C, the electrode 2 layer 310 may be segmented. As aresult, the changes in gray tone in the EPD film layer 308 will appearto be segmented as well. Alternatively, if the electrode 2 310 is asingle continuous sheet, the change in gray tone in the EPD film layer308 will be continuous as well. It should be appreciated that bothelectrode 1 306 and electrode 2 310 may be transparent, and all thelayers (e.g., layers 302, 304, 310 etc) may be transparent, such thatthe display can be viewed from either orientation or directions.

In another embodiment, FIG. 3D illustrates a cross sectional view ofanother display 312 in accordance with the subject matter presentedherein. This display 312 differs from the display illustrated in FIG. 3Ain that only a portion of the piezoelectric film layer 318 overlaps withthe electrode 1 316 layer. In this configuration, the piezoelectric filmlayer 318 can avoid being placed in a neutral plane position, such thatbetter images may be generated from the piezoelectric film 318. Inaddition, the piezoelectric film layer 318 may be a metalized piezo filmand may be covered by a metal layer 320. In some embodiment, a firstsemi-conductive layer 314 may be positioned between the metal layer 320and the electrode 1 layer 316. And another second semi-conductive layer322 may be positioned between the piezoelectric film layer 318 and anelectrode 2 layer 324. It should be appreciated that all the layerspresented herein, including the electrode 1 316 and electrode 2 324layers may be transparent, such that this display may be viewed fromeither direction or orientation.

In yet another embodiment, in a configuration similar to thatillustrated in FIGS. 1 and 2A, but a semi-conductive layer 402 may beplaced between an electrode 2 layer 404 and a piezo film layer 406 andan EPD film layer 408, as shown in FIG. 4. This semi-conductive layer402 may insulate the piezo film layer 406 and the EPD film layer 408from electrode 2 404. Similarly, the display illustrated in FIG. 3A maybe modified to include an additional semi-conductive layer to insulatethe piezo film and the EPD film from electrode 2. Among the variousconfigurations, the display illustrated in FIG. 4 demonstrated the bestCR performance at 18. In any case, the display configurations hereinenables one to construct a piezo-electricity driven device with athickness less than 50 um, and also greatly simplifies the devicestructure and makes the display more sensitive to smaller appliedphysical stress.

FIG. 5 illustrated another design 500 of a display. This display 500 issimilar to the one shown in FIG. 3A except an additional semi-conductivelayer 502 is placed between the piezoelectric layer 504 and theelectrode 2 layer 506. A comparison of the CR ratio between the variousdesigns are illustrated in Table 3 below.

TABLE 3 Comparative CR Response of display on strain change Piezo filmdirectly contact Contrast Ratio: 1.7 with both electrodes FIG. 1Contrast Ratio: 7 FIG. 3A Contrast Ratio: 12 FIG. 4 Contrast Ratio: 18FIG. 5 Contrast Ratio: 14

It should be appreciated that all the layers presented in FIGS. 4 and 5,including the electrode 1 and electrode 2 layers may be transparent,such that these displays may be viewed from either direction ororientation.

It should also be noted that, referring to the display configurationsillustrated in FIGS. 1-5, a conductive path is complete between theelectrode 1 and electrode 2 and the piezoelectric material layer and theEPD film layer, no other conductor or electrodes is needed between theelectrode 1 and electrode 2. This effectively reduces the overallthickness of the device, as well as improves the CR ratio of thedisplay.

FIGS. 6 and 7 illustrate embodiments of piezo electrophoretic displaysthat may be configured to display various patterns, such as the jigsawpattern in FIG. 6 and the star shaped pattern in FIG. 7. In FIG. 6, adisplay 600 may include a plurality of electrodes 602 design totransport charges to electrophoretic display mediums 604 s and 606 s. Inthe embodiment illustrated in FIG. 6, the display medium 604 is of redcolor and the display medium 606 is of black color. It should beappreciated that other colors may be conveniently adopted. In thisconfiguration, electrodes 602 on the top portion of the display may beconnected to the black colored display mediums 606, and the electrodes602 of the bottom portion may be connected to the red colored displaymediums 604. In use, when a force is being applied to the display 600,the display mediums 606 and 604 may display both the black and redcolor. This particular configuration illustrated in FIG. 6 can beprinted using conductive material, greatly simplify the manufacturingprocess.

In some other embodiments, a piezo electrophoretic display in accordancewith the subject matter disclosed herein may be combined with anotherapparatus, such as a currency bill illustrated in FIG. 8. In thisembodiment, a display may be affixed to one end of a bill, and whenphysical stress is applied, the display can switch between one or moregraytones. In this fashion, a user may easily distinguish a genuine billfrom a counterfeiting one. As mentioned above, the electrodes for thedisplay may be segmented, and the resulting gray tone of the EPDmaterial layer may appeal segmented. Alternatively, the electrodes forthe display may be a continuous sheet, and the resulting gray tone ofthe EPD material may vary in a continuous fashion.

Methods of Manufacturing

FIG. 9 illustrates a cross sectional view of yet another embodiment of apiezoelectric display 910 in accordance with the subject matterpresented herein. As shown in FIG. 9, the EPD layer 900 may partiallyextend underneath a piezo-electric material 902 to substantially overlapand ensuring a secured connection with the piezo-electric material 902.In this embodiment, the EPD layer 900 may have one portion havingmicro-cells 906 and another portion that is substantially flat 904 andconfigured for establishing a connection with the piezoelectric material902. In this configuration, the piezo-electric material 902 ispositioned to overlap on the substantially flat portion 904, ensuring agood connection with the EPD layer 900. This configuration canadvantageously establish a strong connection between the piezo-electricmaterial 902 and the EPD layer 900. For example, this configurationoffers a robust connection between the piezo-electric material 902 andthe EPD layer 900 that is capable of withstanding repeated bending orapplied stress onto the display device 910. Additionally, an adhesivelayer 908 may be placed between the piezoelectric material layer 902 andthe conductor 912. In another embodiment, the piezoelectric material 902can be circular in shape and surrounds the EPD material 900.Furthermore, as illustrated in FIG. 9, the piezo-electric material 902and the EPD layer 900 may be sandwiched between two layers of conductorsor conducting materials, and all the above mentioned layers and materialmay be positioned on a substrate that can be flexible. It is preferredthat the substrate be less than 10 micron in thickness to make theoverall device thin. In some embodiments, ITO/PET may be used herein assubstrate. In some other embodiments, flexible and transparentconductive coatings may be used, such as PEDOT:PSS, graphene, carbonnanotubes or silver nano wires. In yet some other embodiments, a barrierlayer may be sputtered onto the substrate layer (e.g., PET) beforecoating the conductive layer to provide a barrier to the ink solvent, asshown in FIG. 10. In some cases, this barrier layer may be SiOx. Sincethe substrate in this case is thin, the barrier layer may also be coatedonto the other side of the substrate. Additionally, other optical layersmay be printed onto the substrate for decoration purposes. In someembodiments, the carrier film may be discarded after the display havebeen assembled. And the rest of the display, without the carrier film,may be integrated with other structures. It should be appreciated thatall the layers presented herein, including the electrode 1 and electrode2 layers may be transparent, such that this display may be viewed fromeither direction or orientation.

FIG. 11A illustrates a top view of the EPD layer 900 of FIG. 9. Asshown, the EPD layer 900 may be manufactured by pattern micro-cellstructures onto only portions of the layer 900, while leaving the otherportion substantially flat. In this fashion, the substantially flatportions 1102 without the micro-cells (i.e., a separate portion 1102 isdesignated to have microcell structures) may be used to createconnections with the piezo-electric layer as shown in FIG. 9. Thismethod of manufacturing offers several advantages. Firstly, it is easierto fabricate the EPD layer in this fashion, where the contacting portion(i.e., the substantially flat portion) and the micro-cell portion 1102are fabricated at the same time, compared to an alternative method wherethe fabrication of the two portions are done separately. Secondly, asthe substantially flat contact portion 1100 and the micro-cell portion1102 are fabricated together, they are more robust structurally, whichleads to a better connection between the EPD layer and thepiezo-electric layer, as well as a more durable display device. FIG. 11Billustrates a cross sectional view of the EPD layer as shown in FIG.11A. The EPD layer may include a first portion 1104 with micro-cellspatterned and a flat portion 1106 with no micro-cells. In practice, thesubstantially flat portion 1106 and the micro-cell portion 1104 may bepatterned at the same photolithography step. In some embodiments, oncethe patterns have been defined, and after an embossing step, strips ofrelease liners may be laminated on to the substantially flat portion,where the thickness of the release liner may be the same of themicro-cell height. It is preferred that the surface energy of therelease liner to be sufficiently high such that the sealing layer willnot de-wet on the top of the release liner, and in some embodiments, thesurface energy may be tuned to a particular level depending on theapplication. The release liner in this case may include poly vinylalcohol or other water soluble polymers. Furthermore, after a filing andsealing step, the release liner may be removed together with the ink andsealing layer on top of it to expose the flat area underneath. Inpractice, removing the release liners will remove the sealinglayer/material and ink from the substantially flat portion of the EPDlayer. This process can ensure a substantially clean break of the inkand sealing material from the micro-cell portion 1104. A piece ofnon-metalized piezo film may be laminated onto the flat. The totalthickness of piezo film and adhesive layer may be similar to the totalthickness of the sealing layer and the micro-cells. In addition, a pieceof adhesive layer may be laminated onto the release liner and onto thefull display panel. A in line humidification or off line chamberhumidification step may be used to ensure good optical performance ofthe display. In practice, after the patterns have been defined in FIGS.11A and 11B, the structure may be cut along the A′A′ line to createdisplays.

In some embodiments, a method for producing a display as describe abovemay include producing a layer of electrophoretic display material havinga first portion 1102 and a second portion 1100, the first portion 1102having a plurality of micro-cells and the second portion 1100 beingsubstantially flat. The method may further include providing apiezoelectric material, and aligning the piezoelectric material to thesecond portion of the electrophoretic display material such that thepiezoelectric material substantially overlaps with the second portion.In some embodiments, the first 1102 and second 1100 portions of theelectrophoretic material are produced using a single photolithographystep. The method may further include placing the electrophoretic displaymaterial and the piezoelectric material onto a substrate, where thesubstrate may be flexible. In some embodiments, the method may furtherinclude providing a conductive electrode onto the substrate, andproviding a barrier layer between the conductive electrode and thesubstrate. In some embodiments, after the producing a layer ofelectrophoretic display step, the method may further include providing alayer of release liner, where the release liner has a height that issubstantially similar to that of the plurality of micro-cells.

Furthermore, another second electrode may be printed on top of thesubstrate as shown in FIG. 6. To connect the second electrode to the EPDmaterial, conducive ink may be used to pattern conductive traces orlines. In some embodiments, the pattern may contain two portions. Afirst portion may be printed as small strips and a second portion may bea two pixel pattern. Where each pixel may be connected to one or twosmall stripes suing conductive ink. These patterns may then besubsequently aligned and laminated onto the above mentioned FPL with thepiezoelectric film on top of the small stripes.

FIGS. 12A and 12B illustrate another embodiment of an electrophoreticdisplay 1200 utilizing piezoelectric material. As shown, a piezoelectricmaterial layer 1202 may be stacked with a display medium layer 1204(e.g., an electrophoretic medium layer) to form a display. Twoelectrodes, electrode 1 1206 and electrode 2 1208 may be positioned onthe two sides as shown in FIGS. 12A and 12B to sandwich the EPD layer1204 and the piezoelectric material layer 1202 to complete a conductivepath for the charges. In some embodiments, the electrode 2 1208 may be ametal on piezoelectric film or a laminated conductive adhesive on piezofilm. In this configuration, no other connections is needed to drive theelectrophoretic display material 1204.

In use, when a force is applied onto the piezoelectric material layer1202, charge separation occurs within the piezoelectric material 1202.The charge on the interface of the electrophoretic display medium layer1204 and the piezoelectric material layer 1202 can induce the charges onthe EPD film and the electric field passes through the EPD to make theparticles move. FIG. 12B illustrates a view of the charge distribution.

In yet another embodiment, to achieve an even better contrast ratio,piezo films with opposite poling directions may be positioned in a sideby side configuration, as illustrated in FIGS. 13A and 13B. In use, PZ1and PZ2 can produce opposite voltages under an applied force, FIG. 13Bshows one embodiment of charge distribution when force is applied. Itshould be appreciated that all the layers presented herein in FIGS.12A-13B, including the electrode 1 and electrode 2 layers may betransparent, such that this display may be viewed from either directionor orientation.

The embodiments shown in FIGS. 12A-13B not only reduces the overalldevice thickness to be less than 50 micro-meters, but also vastlyimprove the CR. It furthermore simplifies the device structure and makesthe display device more sensitive to small strain changes.

Latent Images

In some embodiments, displays with structures that's similar to or basedon the configurations illustrated in FIG. 12A or FIG. 1 may be modifiedto display latent images. Illustrated in FIG. 14A is a display device1400 similar to the one presented in FIG. 12A, but with images or shapeslaminated or printed onto either the electrode 1 1406 or electrode 21408. It should be appreciated that the configuration presented in FIG.14A is for illustrating the concept as other configurations can beeasily adopted to achieve the same effect. In practice, every layer ofthe display 1400 may be transparent (e.g., layers 1402, 1404, 1406, 1408etc), even the adhesive layers and the electrodes 1 and 2 layers, suchthat this display can be viewed from either direction or orientation.

In some embodiments, images or shapes may be printed or laminated onto awhite background and onto either the electrode 1 1406 or electrode 21408, and viewed from an opposite side. In use, when the EPD layer 1404is showing white color, the printed image or shape will be hidden (i.e.,see FIG. 14B), and when the EPD 1404 switches to another color whenforce is applied, the printed image or shape may be displayed (i.e., seeFIG. 14C).

In yet another embodiment, dark colored images or shapes may be producedonto either electrode 1 1406 or electrode 2 1408 without a backgroundand be viewed from an opposite side. In this configuration, when thedisplay 1400 is position over a black background, as illustrated in FIG.14D, the printed image or shape will remain hidden no matter how the EPD1404 is bend. Alternatively, when the display 1400 is positioned over awhite or light colored background, the printed image or shape will showup and it is more obvious when the EPD 1404 switches to a darker color,as illustrated in FIG. 14E.

In yet another embodiment, as illustrated in FIG. 15A, images or shapesmay be produced outside electrode 1 s 1502, 1504 or either EPD display 11506 and EPD display 2 1508. The two EPD displays 1506, 1508 may beintegrated together using a transparent adhesive material. When force isapplied (e.g., bending), both EPD display 1 1506 and EPD display 2 1508can change color. When EPD display 2 1508 turns dark and EPD display 11506 turns white, the printed image or shape will not show up, asillustrated in FIG. 15C. Alternatively, when EPD display 2 1508 turnswhite and EPD display 1 1506 turns dark, the printed image or shape willsurface, as illustrated in FIG. 15B.

It should also be noted that, referring to the display configurationsillustrated in FIGS. 9-14A, a conductive path is complete between theelectrode 1 and electrode 2 and the piezoelectric material layer and theEPD film layer, no other conductor or electrodes is needed between theelectrode 1 and electrode 2. And in the case of the display illustratedin FIG. 15, no additional conductor or electrode is needed for each ofthe stacked displays 1506 and 1508. This effectively reduces the overallthickness of the device, as well as improves the CR ratio of thedisplay.

It will be apparent to those skilled in the art that numerous changesand modifications can be made to the specific embodiments of theinvention described above without departing from the scope of theinvention. Accordingly, the whole of the foregoing description is to beinterpreted in an illustrative and not in a limitative sense.

The invention claimed is:
 1. An electro-optic display comprising: alayer of electrophoretic material; a first conductive layer; apiezoelectric material positioned between the layer of electrophoreticmaterial and the first conductive layer, wherein the piezoelectricmaterial overlaps with only a first portion of the layer ofelectrophoretic material, while the first conductive layer overlaps withall the piezoelectric material and a second portion of the layer ofelectrophoretic material that does not overlap with the piezoelectricmaterial, and wherein the first portion of the layer of electrophoreticmaterial comprises a first plurality of micro-cells and has a firstelectrical resistance and the second portion of the layer ofelectrophoretic material comprises a second plurality of micro-cells andhas a second electrical resistance; and an adhesive layer positionedbetween the piezoelectric material and the layer of electrophoreticmaterial, wherein the adhesive layer has a resistivity between 10⁸Ohm*cm and 10¹² Ohm*cm.
 2. The electro-optic display of claim 1 furthercomprising a second conductive material positioned next to the layer ofelectrophoretic material and opposite from the piezoelectric material.3. An electro-optic display comprising: a layer of electrophoreticmaterial; a semi-conductive material having a resistivity ofsubstantially 10² to 10¹² Ohm*cm; and a piezoelectric material stackedwith the semi-conductive material, wherein the piezoelectric materialand the semi-conductive material are positioned side by side with thelayer of electrophoretic material.
 4. The electro-optic display of claim3 further comprising a first conductive layer overlapping with thepiezoelectric material and the electrophoretic material.
 5. Theelectro-optic display of claim 4 further comprising a second layer ofsemi-conductive material between the first conductive layer and thepiezoelectric material and the electrophoretic material.
 6. Theelectro-optic display of claim 3 further comprising a second conductivelayer overlapping with the semi-conductive material and theelectrophoretic material.
 7. An electro-optic display comprising: alayer of electrophoretic material; a first layer of piezoelectricmaterial; and a second layer of piezoelectric material, the first andsecond layers of piezoelectric material positioned side by side, whereinthe first layer of piezoelectric material overlaps with only a firstportion of the layer of electrophoretic material while the second layerof piezoelectric material overlaps with a second portion of the layer ofelectrophoretic material that does not overlap with the first layer ofpiezoelectric material, wherein the first and second layers ofpiezoelectric material have opposite poling directions.
 8. A method forproducing a display comprising: producing a layer of electrophoreticdisplay material having a first portion and a second portion, the firstportion having a plurality of micro-cells and the second portion beingsubstantially flat; providing a piezoelectric material; and aligning thepiezoelectric material to the second portion of the electrophoreticdisplay material such that the piezoelectric material substantiallyoverlaps with the second portion and is positioned side by side with theplurality of micro-cells.
 9. The method of claim 8, wherein the firstand second portions of the electrophoretic material are produced using asingle photolithography step.
 10. The method of claim 8 furthercomprising placing the electrophoretic display material and thepiezoelectric material onto a substrate.
 11. The method of claim 10wherein the substrate is flexible.
 12. The method of claim 10 furthercomprising providing a conductive electrode onto the substrate.
 13. Themethod of claim 12 further comprising providing a barrier layer betweenthe conductive electrode and the substrate.
 14. The method of claim 8after the producing a layer of electrophoretic display step, furthercomprising providing a layer of release liner.
 15. The method of claim14 wherein the release liner has a height that is substantially similarto that of the plurality of micro-cells.